Electrical Characterization of Graphene-based e-Tattoos for Bio-Impedance-based Physiological Sensing

Bio-impedance (Bio-Z) is a promising method to measure a plurality of physiological observations from the human body. The principal challenge, however, remains in the electrodes. Wet-electrodes are inconvenient to wear and drycontact electrodes do not provide sufficient robustness. The objective of this work is to demonstrate the feasibility of leveraging graphene-based electrodes to establish intimate contact with the skin while not introducing any discomfort to the user. Our proposed electrodes are ultrathin, soft, transparent, and can potentially remain on the skin at the same location over an extended period, while offering robust measurements. In this paper, we present the characterization of the proposed ultrathin and skin-conformable graphene-based electronic tattoos (GETs) in continuous Bio-Z measurements. Our bilayer GETs (biGETs) provide an average of contact impedance with the skin at 10 kHz, improving the contact impedance acquired from the traditional dry electrodes. Moreover, Bio-Z measurements with the GETs show less variation (3.6 average standard deviation, 6.5 maximum standard deviation with biGET) due to its stable contact to the reference wet electrode measurements (4.1 average standard deviation and 7.5 maximum standard deviation with wet electrodes). Compared to the traditional electrode structures, our proposed GETs provide better contact impedance, good adherence to the skin, robustness in sensing, and additional comfort and breathability.